A “flip-chip LED” technology means one in which the luminous element, usually an LED, is mounted upside down as shown in FIG. 1a. First industrial property rights in this field trace back to Matsushita (e.g., JP 57 092881 A1) and date from the early 1980's. Today, there are more than 1000 patent publications relating to this topic.
In this connection, reference may be made to US 2011 062469 A1 (Philips). This document relates to a light-emitting unit consisting of an LED, a lens, a window element, a bond at the interface between the lens and window element, wherein the window element is bonded to the lens.
US 2012 153306 A1 (YAO) discloses a light-emitting diode (LED) chip, comprising: a flip-chip LED and a lens applied to the topmost surface of the flip-chip LED, wherein said lens contains a non-polymeric material, and essentially no polymer materials come into contact with the LED chip.
From US 2011 062471 A1 (Bierhuizen). This application relates to an LED module with a lens having a modular structure, wherein said LED module is adhesively bonded to the support.
WO 2009/132837 A2 (Schott) claims a converter component for the radiation emitted and/or to be received by an opto-electronic functional element, preferably by an LED, for mounting onto an opto-electronic functional element comprising at least one converter for converting the emitted radiation and/or the radiation to be received, and at least one optical component, said converter and said optical component being adjacent and bonded to one another at least over segments thereof.
FC LEDs have a number of important advantages over the conventional products, in particular, they ensure a quicker heat dissipation, which significantly increases the service life. Also, FC LEDs do not require any devices to direct the light into a particular direction, and they ensure a high image brightness even in reflection, as schematically represented in FIGS. 1b and 1c. 
Another important aspect is the fact that FC LEDs can be produced more easily and more quickly, because after the EPI wafer stage, only die bonding and a modulation are required to finish the component. Thus, the steps of wire bonding and encapsulating the phosphor, in particular, are saved.
The chips are mostly enclosed by transparent lens-shaped hollow bodies, wherein plastics, predominantly polydimethylsiloxanes, are usually employed as the material. These have prevailed especially in the known and established nitride-based compound semiconductor chips, because they do not absorb the outgoing radiation and therefore show no, or only very little, signs of wear.
However, silicones have remarkably low refractive indices, typically around 1.40 to 1.41. This means that there usually is a significant difference in the refractive indices between the chip and the casing, with the consequence that the emission of radiation from the chip is greatly reduced.
In the past, it was tried to solve this problem by chemically modifying the polydimethylsiloxanes, for example, by incorporating aromatic groups. These approaches are actually rather counterproductive, because the modification of the siloxanes ultimately leads to an increase of the absorption of the light exiting the chip into the silicone body, so that the outgoing radiation is reduced rather than enhanced, the silicone casing increasingly loses its transparency, and the absorption losses can be increased thereby.
Another disadvantage in connection with the use of silicones as casings for FC LEDs is the fact that the refractive index becomes lower as the temperature increases, that they have a high permeability for gases and water, and exhibit a low hardness.
Thus, it has been the object of the present invention to provide illuminating devices of the flip-chip LED type that overcome the described drawbacks of the prior art. In particular, the components should be equipped with casings having a similar refractive index as the composite of support and luminous element, be resistant to temperature and environmental influences, have no permeability to gases and water, and possess a hardness higher than that of polysiloxanes.